1. Field of the Invention
The present invention relates to the field of electrotechnology, especially the field of electric drives, and concerns brushless drives.
2. Description of the Background Art
Electric motors, in which a rotor rotates in the magnetic field of a stator, whereby the rotor has rotor windings that can be supplied with alternating current strengths to excite a rotor field, are widespread in the field of electric drives. The electric current is supplied to the rotor windings via an electromechanical commutator device with current-conducting brushes, which brush the rotor-side commutator lamellae during the rotation of the rotor.
In many fields, these drives, which require a commutator device, have been replaced by so-called brushless electrical drives that have permanent magnets in the rotor, which move in the rotating magnetic field of the stator windings. A complex control of the currents through the stator windings is necessary to drive such motors, whereby it is typical to feed the stator windings with pulse-width-modulated voltage signals, generated by semiconductor switches.
For optimal control of such a brushless drive, it is particularly necessary in the startup phase to determine the rotor's angular position. Slippage can be minimized and the rotational speed optimally controlled in this way during operation of the drive.
It is known for determining the position of the rotor to use at least one Hall sensor for measuring the magnetic field strength, the sensor being disposed on the stator and registering the movement and position of the rotor's magnetic poles. During operation of the drive, the currents induced in the phase windings by the relative movement of the rotor can be measured and the position and rotational speed can be determined from them.
A task that is especially difficult to solve is to determine the position of the drive at very low rotational speeds or when at rest without the use of sensors and/or particularly to bring the rotor into a target start position.